Pump control means

ABSTRACT

A control means for use with a counterbalanced pump unit including in general a frame, a pump rod leading to a bottom hole pump, counterweights movably mounted from the frame for offsetting the weight of the pump rod, means for driving the counterweights between upper and lower positions, and means for causing the pump rod to move relative to the counterweights. The control means includes cammed means mounted to the frame, cam means mounted to the counterweights and coacting with the cammed means as the counterweights are driven between the upper and lower positions, and linkage means connecting the cammed means to the means for driving the counterweights to regulate the means for driving the counterweights as the cam means coacts with the cammed means causing the counterweights to move between the upper and lower positions in a smooth, even rate.

United States Patent [191 Lawson 1 Mar. 4, 1975 1 PUMP CONTROL MEANS[76] Inventor: Joseph M. Lawson, PO. Box 518, [57] ABSTRACT Natchez, i39120 A control means for use with a counterbalanced pump unit includingin general a frame, a pump rod leading Flled: 1974 to a bottom holepump, counterweights movably [211 App} 45 52 mounted from the frame foroffsetting the weight of the pump rod, means for driving thecounterweights between upper and lower positions, and means for [52]11.8. C1 60/382, 60/446, 74/8920 causing the pump rod to move relativeto the Counter [51] Int. Cl. .l F16h 39/46, Fl5b 15/18 weights The comm]means includes cammed means [58] Field of Search 91/216 B, 218, 327;mounted to the frame, Cam means mounted to the 74/8922 8920; 60/382counterweights and coacting with the cammed means as the counterweightsare driven. between the upper References C'ted and lower positions, andlinkage means connecting the UNITED STATES PATENTS cammed means to themeans for driving the counter- 36.656 10/1864 Knowles 91/327 weights toregulate the means for driving the counter- 407,338 7/1889 Downie l l91/327 weights as the cam means coacts with the cammed 904,528 11/1908Pierce s r r 91/216 B means causing the counterweights to move between 23 1 x32 Bender 8 52 the upper and lower positions in a smooth, evenrate. 3318 9 awson V r r M V n Primary E.\'aminerPaul E. MaslouskyAttorney, Agent, or Firm-John R. Walker, 111

6 Claims, 5 Drawing Figures PUMP CONTROL MEANS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally topumping units and more specifically to control means for use withcounterbalanced pumping units for pumping crude oil or the like fromwells.

2. Description of the Prior Art The following U.S. patents disclosecounterbalanced pump units: Bender, U.S. Pat. No. 3,248,958 and Lawson,U.S. Pat. No. 3,482,399. Neither of the above patents disclose orsuggest the present invention.

The U.S. Pat. No. 3,248,958 reference discloses a counterbalanced pumpunit which is controlled by means of limit switches. That is, as thetravel of the counterweights is completed in one direction, a limitswitch is tripped causing a reversal of the movement of thecounterweights. The U.S. Pat. No. 3,482,399 reference discloses acounterbalanced pump unit which is controlled by means of cams. That is,as the travel of the counterweights is completed in one direction, a camis contacted and causes an immediate reversal of the movement of thecounterweights.

The known prior counterbalanced pump units are disadvantageous in thatthey are highly susceptible to failure due to pump rod breakage causedby the high velocities, high and low peak loads, frequent reversals, rodstretch, and overtravel common to counterbalanced pump units.

SUMMARY OF THE INVENTION The present invention is directed towardsovercoming the problems and disadvantages in counterbalanced pump units.More specifically, the present invention minimizes pump rod stretch and,thereby, minimizes failure of the pump unit due to pump rod breakage.

The concept of the present invention is to provide a control meansadapted to be used with a counterbalanced pump unit which causes thecounterweights to revese directions in a smooth, even rate thereby preventing the builk-up of stress or the like in the pump rod. The controlmeans includes, in general, cam means, cammed means for coacting withthe cam means as the counterweights are driven between upper and lowerpositions, and linkage means for connecting the cammed means to meansfor driving the counterweights to cause the counterweights to movebetween the upper and lower positions in a smooth, even rate.Preferably, stop means is included to prevent over travel of the cammedmeans.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat simplified frontelevational view of a counterbalanced pump unit including the controlmeans of the present invention.

FIG. 2 is an end elevational view of FIG. 1.

FIG. 3 is detailed view of a portion of the linkage means of the presentinvention.

FIG. 4 is a detailed view of the stop means of the present invention.

FIG. 5 is a detailed view ofa portion of the means for driving thecounterweights of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The control means 11 of thepresent invention is for use with a counterbalanced pump unit such asthe pump unit 13 illustrated known to those skilled in the art. Ingeneral, the counterbalanced pump unit 13 includes a frame 15, a pumprod 17 leading to a bottom hole pump (not shown) in a typical oil well19 or the like, counterweights 21 movably mounted from the frame 15preferably by means of a carriage 23, means for driving thecounterweights 21 between upper and lower positions, and means forcausing the pump rod 17 to move relative to the counterweights 21. Theframe 15 preferably includes a crown post 15', a rear post 15', and ahorizontal beam 15". The means for driving the counterweights 21 betweenupper and lower positions preferably includes a motor 25, a hydraulicpump 27, a hydraulic cylinder 29, a piston rod 31, and hydraulic lines33 between the hydraulic pump 27 and the piston rod 31. The hydrauliccylinder 29 and the piston rod 31 are preferably of the type disclosedin the U.S. Pat. No. 3,482,399 reference with the carriage 23 beingattached to the hydraulic cylinder 29 by any means well known to thoseskilled in the art such as the gimbal assembly disclosed in the U.S.Pat. No. 3,482,399 reference, with the upper end of the piston rod 31attached to the frame 15 through an anchor joint 35 allowing universalpivot pin movement of the piston rod 31 while preventing any verticalmovement thereof, and with the lower end of the piston rod free forlateral movement.

The means for causing the pump rod 17 to move relative to thecounterweights 21 preferably includes first and second sheaves 37, 39rotatably mounted on the upper portion of the crown post 15' 0f theframe 15; third and fourth sheaves 41, 43 rotatably mounted on thehydraulic cylinder 29; a pump rod hanger 45 fixedly attached to theupper end of the pump rod 17; a first flexible cable 47 having a firstend fixedly attached to the pump rod hanger, having a body portionextending around the first sheave 37 and the third sheave 45, and havinga second end fixedly attached to the horizontal beam 15' of the frame15; and a second flexible cable 49 having a first end fixedly attachedto the pump rod hanger 45, having a body portion extending around thesecond sheave 39 and the fourth sheave 43, and having a second endfixedly attached to the horizontal beam 15" of the frame 15. As thusconstructed, the means for causing the pump rod to move relative to thecounterweights 21 gives the pump rod 17 twice the travel of thecounterweights 21. However, it should be noted that any suchconstruction well known to those skilled in the art may be used.

The control means 11 of the present invention includes in general cammedmeans 51 mounted to the frame 15, cam means 53 fixedly mounted on thecounterweights 21 for coacting with the cammed means 51, and linkagemeans 55 connecting the cammed means 51 to the means for driving thecounterweights 21 for regulating the means for driving thecounterweights 21 to cause the counterweights 21 to move between theupper position and the lower position in a smooth, even rate. The cammedmeans 51 includes a shaft 57 rotatably mounted preferably to the rearpost 15" of the frame 15 by support members 5'9, a first cylindricalcammed member 61 fixedly mounted on a first end 57' of the shaft 57having a cam surface 61, and a second cylindrical cam 63 fixedly mountedon a second end 57" of the shaft 57 having a cam surface 63'.

The cam means 53 includes in general an arm 65 fixedly mounted to thecounterweights 21 and a roller 67 rotatably mounted on the arm 65 forcoacting with the cam surfaces 61 63 of the first and second cylindricalcammed members 61, 63.

The linkage means 55 includes, in general, a first rigid member 69 (FIG.3) fixedly connected to the shaft 57 for rotation therewith and a secondrigid member 71 having a first end pivotally mounted to the first rigidmember 69 and having a second end pivotally mounted to the hydraulicpump 27. As thus constructed, the linkage means transfers movement ofthe shaft 57 to the hydraulic pump 27 to control the output of thehydraulic pump 27 and thereby controls the movement of thecounterweights 21. Preferably, the second rigid member 71 includes aturnbuckle means 73 and a flexible connection 75.

The control means 11 includes flywheel means 77 coactively mounted tothe shaft 57 for temporarily storing the momentum of the rotation of theshaft 57 to cause rotation of the shaft 57 to continue after thecounterweights 21 have reached the upper or lower position. The flywheelmeans 77 preferably includes a first sprocket 79 fixedly attached to theshaft 57, a second sprocket 81 fixedly attached to a second shaft 83that is rotatably mounted from the rear post of the frame 15 by supportmembers 85, a continuous chain 87 connecting the first sprocket 79 tothe second sprocket 81, and a flywheel 89 fixedly mounted to the secondshaft 83. The first sprocket 79 is of a larger diameter than the secondsprocket 81 so that one complete revolution of the shaft 57 will causemore than one complete revolution ofthe second shaft 83. Preferably, theratio between the first sprocket 79 and the second sprocket 81 is 15-20to 1. A clutch means 91 is preferably provided adjacent the flywheel 89to dissipate excessive momentum of the flywheel 89 after the rotation ofthe shaft 57 is stopped.

The control means 11 is preferably provided with a stop means 93 forstopping the rotation of the shaft 57 after a fixed amount of rotation.The stop means 93 preferably includes an arm portion 95 fixedly mountedto the shaft 57, a platform member 97 fixedly mounted to supportstructure such as the frame 15 or the like adjacent the arm member 95,and first and second stop members 99, 101 mounted on the platform member97 so that when the arm member 95 is rotated a fixed amount such as 70,it contacts either the first or second stop member 99, 101 and isthereby prevented from further rotating. Preferably, the first and.second stop members 99, 101 are manually adjustable to allow the amountof rotation of the arm member 95 and, therefore, the shaft 57 to bevaried or graduated. More specifically, the platform member 97 ispreferably provided with a plurality of apertures 99' for selectivelyreceiving the first stop member 99 and a plurality of apertures 101' forselectively receiving the second stop member 101. The apertures 99', 101are located at predetermined positions on the platform member 97 so thatthe first and second stop members 99, 101 may be adjusted to allow thearm member 95 to rotate various amounts such as 60, 70or 80. it shouldbe noted that the first and second stop members 99, 101 can beselectively received in the apertures 99, 101' by any means well knownto those skilled in the art such as by screw threads or the like.

The hydraulic pump 27 is of the well known variable displacement typewhich is controlled by a manually operated servo valve 103 (See, forexample, US. Pat. No. 3,482,399). The servo valve 103 regulates both thevolume output and the direction of flow from the pump 27. In general,the servo valve 103 includes a control arm 105 having a first definiteposition in which the volume output of the pump 27 is at its maximum andin which the direction of flow is in a first direction, having a seconddefinite position in which the volume output of the pump 27 is at itsmaximum and in which the direction of flow is in a second directionopposite from the first direction, and having a definite neutralposition between the first and second definite positions in which thereis no flow from the pump 27. As the control arm 105 is moved between thefirst definite position and the definite neutral position or the seconddefinite position and the definite neutral position, the volume outputof the pump 27 is varied by an amount proportional to the amount ofmovement. That is, as the control arm 105 is moved away from thedefinite neutral position towards either the first or second definiteposition, the volume output ofthe pump 27 is increased until the volumeoutput is at a maximum when the control arm 105 is at either the firstor second definite position. On the other hand, as the control arm 105is moved toward the definite neutral position away from either the firstor second definite positions, the volume output of the pump 27 isdecreased until there is no flow when the control arm is at the definiteneutral position. It should be noted that the servo valve 103 includesfirst and second stop portions 107, 109 for preventing movement of thecontrol arm 105 beyond the first or second definite position. inaddition, the stop portions 107, 109 are preferably of variable sizes toalter the positions of the first and second definite positions therebyvarying the maximum volume output of the pump 27. That is, by increasingthe size of the stop portions 107, 109 the first and second definitepositions are moved closer to the definite neutral position therebydecreasing the maximum volume output of the pump 27. The first andsecond stop portions 107, 109 may be of different sizes to cause themaximum volume output of the pump to be different between the first andsecond definite positions. Similarly, the turnbuckle means 73 may beutilized to vary the maximum volume output of the pump 27. That is,increasing or decreasing the length of the second rigid member 71 willcause the movement of the control arm 105 to be increased in onedirection and decreased in the other thereby varying the amount ofcontrol the linkage means 55 has over the pump 27.

The operation of the present invention is as follows: as thecounterweights 21 approach the upper position, the roller 67 of the cammeans 53 contacts the cam surface 61' of the first cylindrical cammedmember 61 causing the shaft 57 to rotate. As the shaft 57 rotates, thelinkage means 55 moves the control arm 105 of the servo valve 103 awayfrom the first definite position towards the definite neutral positioncausing the volume output of the pump 27 to decrease, thereby slowingdown the movement of the counterweights 21. As the roller 67 of the cammeans 53 continues to cause the first cylindrical cammed member 61 torotate the shaft 57, the control arm 105 will be moved to the definiteneutral position in which there is no flow from the pump 27 and, thus,the movement of the counterweights 21 will stop. However, due to theflywheel means 77, the rotation of the shaft 57 will continue causingthe control arm 105 to be moved past the definite neutral positiontowards the second definite position so that the flow from the pump 27will cause the counterweights 21 to begin movement towards the lowerposition. The shaft 57 will continue its rotation until stopped by thestop means 93. When the stop means 93 causes the shaft 57 to stoprotating, the control arm 105 is in the second definite position and thevolume output of the pump 27 is at its maximum. As the counterweights 21move towards the lower position, the roller 67 of the cam means 53contacts the cam surface 63 of the second cylindrical cammed member 63causing the shaft 57 to rotate in the opposite direction from thatcaused by the coaction of the cam means 53 and the first cylindricalcammed member 61, thereby, causing the control arm 105 to move away fromthe second definite position towards the def inite neutral position.After the control arm 1115 reaches the definite neutral position andcauses the counterweights 21 to stop movement, the shaft 57 continuesrotating because of the flywheel means 77 and causes the control arm 105to move from the definite neutral position towards the first definiteposition thereby causing the counterweights 21 to start movement towardsthe upper position again. The shaft 57 will continue rotating untilstopped by the stop means 93 with the control arm 105 in the firstdefinite position and with the volume output of the pump 27 at itsmaximum. As the counterweights 21 move towards the upper position, theabove described process is repeated.

As thus constructed and operated, the present invention allows movementof the counterweights 21 in a smooth, even rate to prevent failure ofthe pump rod 17 due to stresses being set up in the pump rod 17 as aresult ofthe high velocities, high and low peak loads, frequentreversals, rod stretch, and over travel common to counterbalanced pumpunits. A counterbalanced pump unit 13 having the control means 11 of thepresent invention is capable by the use of direction of flow and volumeoutput variations of the hydraulic pump 27 of maintaining equal speed onthe up and down strokes of the counterweights 21 between the upperposition and the lower position, of maintaining a fast upstroke and aslow downstroke, or of maintaining a slow upstroke and a fastdownstroke. The advantages of maintaining such stroke speeds are wellknown to those skilled in the art.

Although the invention has been described and illustrated with respectto a preferred embodiment thereof, it is not to be so limited sincechanges and modifications may be made therein which are within the fullintended scope of the invention.-

I claim:

1. A control means for use with a typical counterbalanced pump unitincluding in general a frame, a pump rod. counterweights for offsettingthe weight of the pump rod, means for driving the counterweights betweenupper and lower positions, and means causing the pump rod to moverelative to the counterweights, said control means comprising:

a. cammed means for mounting to the frame;

b. cam means for fixedly mounting on the counterweights and for coactingwith said cammed means as the counterweights are driven between theupper and lower positions to cause said cammed means to rotate;

c. linkage means for connecting said cammed means to the means fordriving the counterweights to regulate the means for driving thecounterweights to cause the counterweights to move between the upper andlower positions in a smooth, even rate as said cam means causes saidcammed means to rotate;

d. means for temporarily storing the momentum of the rotation of saidcammed means to cause rotation of said cammed means to continue afterthe counterweights have reached the upper or lower position;

e. stop means for stopping the rotation of said cammed means after afixed amount of rotation; and

f. means for dissipating excessive momentum of said means fortemporarily storing the momentum of the rotation of said cammed meansafter the rotation of said cammed means is stopped.

2. The control means of claim 1 in which said cammed means includes:

a. shaft means for rotatably mounting to the frame,

said shaft means having first and second ends;

b. a first cylindrical cammed member fixedly mounted on said first endof said shaft means for coacting with said cam means when thecounterweights are being driven to the upper position to cause rotationof said shaft means in a first direction; and

c. a second cylindrical cammed member fixedly mounted on said second endof said shaft means for coacting with said cam means when thecounterweights are being driven to the lower position to cause rotationof said shaft means in a second direction.

3. The control means ofclaim 2 in which said linkage means is fixedlyconnected to said shaft means so that when said shaft means is rotatedin the first direction said linkage means causes the means for drivingthe counterweights to drive the counterweights in the upper directionand when said shaft means is rotated in the second direction saidlinkage means causes the means for driving the counterweights to drivethe counterweights in the lower direction.

4. The control means of claim 3 in which said linkage means includesturnbuckle means for varying the length of said linkage means to varythe amount of control over the means for driving the counterweights.

5. A control means for use with a typical counterbalanced pump unitincluding in general a frame, a pump rod leading to a bottom hole pump,counterweights movably mounted on the frame for offsetting the weight ofthe pump rod, means for driving the counterweights between upper andlower positions, and means for causing the pump rod to move relative tothe counterweights, said control means comprising:

a. cammed means including shaft means for rotatably mounting to theframe, a first cylindrical cammed member fixedly mounted on a first endof said shaft means, and a second cylindrical cammed member fixedlymounted on a second end of said shaft means;

b. cam means for fixedly mounting on the counterweights and for coactingwith said first cylindrical cammed member when the counterweights arebeing driven to the upper position to cause rotation of said shaft meansin a first direction and for coacting with said second cylindricalcammed member when the counterweights are being driven to the lowerposition to cause rotation of said shaft means in a second direction;

c. flywheel means coactively mounted to said shaft means for temporarilystoring the momentum of the rotation of said shaft means to causerotation of said shaft means to continue after the counterweights havereached the upper or lower position;

(1. stop means for stopping the rotation of said shaft means after afixed amount of rotation;

e. clutch means for dissipating excessive momentum of said flywheelmeans after the rotation of said shaft means is stopped; and

f. linkage means for connecting said shaft means to the means fordriving the counterweights so that when said shaft means is rotated inthe first direc tion said linkage means causes the means for driving thecounterweights to drive the counterweights in the upper direction andwhen said shaft means is rotated in the second direction said linkagemeans causes the means for driving the counterweights to drive thecounterweights in the lower direction.

6. The combination with a typical counterbalanced pump unit including ingeneral a frame, a pump rod leading to a bottom hole pump,counterweights movably mounted on the frame for offsetting the weight ofthe pump rod, means for driving the counterweights between upper andlower positions, and means for causing the pump rod to move relative tothe counterweights, of control means for controlling the means fordriving the counterweights to allow the counterweights to move betweenthe upper and lower positions with equal or unequal speed in a smooth,even rate, said control ineans comprising:

a. cammed means including shaft means rotatably mounted to the frame, afirst cylindrical cammed member fixedly mounted on a first end of saidshaft means, and a second cylindrical cammed member fixedly mounted on asecond end of said shaft means;

b. cam follower means fixedly mounted on the counterweights for coactingwith said first cylindrical cammed member when the counterweights arebeing driven to the upper position to cause rotation of said shaft meansin a first direction and for coacting with said second cylindricalcammed member when the counterweights are being driven to the lowerposition to cause rotation of said shaft means in a second direction;

c. linkage means connecting said shaft means to the means for drivingthe counterweights so that when said shaft means is rotated in the firstdirection said linkage means causes the means for driving thecounterweights to drive the counterweights in the upper direction andwhen said shaft means is rotated in the second direction said linkagemeans causes the means for driving the counterweights to drive thecounterweights in the lower direction;

d. flywheel means coactively mounted to said shaft means for temporarilystoring the momentum of the rotation of said shaft means to causerotation of said shaft means to continue after the counterweights havereached the upper or lower position;

e. stop means for stopping the rotation of said shaft means after afixed amount of rotation; and f. clutch means for dissipating excessivemomentum of said flywheel means after the rotation of said

1. A control means for use with a typical counterbalanced pump unitincluding in general a frame, a pump rod, counterweights for offsettingthe weight of the pump rod, means for driving the counterweights betweenupper and lower positions, and means causing the pump rod to moverelative to the counterweights, said control means comprising: a. cammedmeans for mounting to the frame; b. cam means for fixedly mounting onthe counterweights and for coacting with said cammed means as thecounterweights are driven between the upper and lower positions to causesaid cammed means to rotate; c. linkage means for connecting said cammedmeans to the means for driving the counterweights to regulate the meansfor driving the counterweights to cause the counterweights to movebetween the upper and lower positions in a smooth, even rate as said cammeans causes said cammed means to rotate; d. means for temporarilystoring the momentum of the rotation of said cammed means to causerotation of said cammed means to continue after the counterweights havereached the upper or lower position; e. stop means for stopping therotation of said cammed means after a fixed amount of rotation; and f.means for dissipating excessive momentum of said means for temporarilystoring the momentum of the rotation of said cammed means after therotation of said cammed means is stopped.
 2. The control means of claim1 in which said cammed means includes: a. shaft means for rotatablymounting to the frame, said shaft means having first and second ends; b.a first cylindrical cammed member fixedly mounted on said first end ofsaid shaft means for coacting with said cam means when thecounterweights are being driven to the upper position to cause rotationof said shaft means in a first direction; and c. a second cylindricalcammed member fixedly mounted on said second end of said shaft means forcoacting with said cam means when the counterweights are being driven tothe lower position to cause rotation of said shaft means in a seconddirection.
 3. The control means of claim 2 in which said linkage meansis fixedly connected to said shaft means so that when said shaft meansis rotated in the first direction said linkage means causes the meaNsfor driving the counterweights to drive the counterweights in the upperdirection and when said shaft means is rotated in the second directionsaid linkage means causes the means for driving the counterweights todrive the counterweights in the lower direction.
 4. The control means ofclaim 3 in which said linkage means includes turnbuckle means forvarying the length of said linkage means to vary the amount of controlover the means for driving the counterweights.
 5. A control means foruse with a typical counterbalanced pump unit including in general aframe, a pump rod leading to a bottom hole pump, counterweights movablymounted on the frame for offsetting the weight of the pump rod, meansfor driving the counterweights between upper and lower positions, andmeans for causing the pump rod to move relative to the counterweights,said control means comprising: a. cammed means including shaft means forrotatably mounting to the frame, a first cylindrical cammed memberfixedly mounted on a first end of said shaft means, and a secondcylindrical cammed member fixedly mounted on a second end of said shaftmeans; b. cam means for fixedly mounting on the counterweights and forcoacting with said first cylindrical cammed member when thecounterweights are being driven to the upper position to cause rotationof said shaft means in a first direction and for coacting with saidsecond cylindrical cammed member when the counterweights are beingdriven to the lower position to cause rotation of said shaft means in asecond direction; c. flywheel means coactively mounted to said shaftmeans for temporarily storing the momentum of the rotation of said shaftmeans to cause rotation of said shaft means to continue after thecounterweights have reached the upper or lower position; d. stop meansfor stopping the rotation of said shaft means after a fixed amount ofrotation; e. clutch means for dissipating excessive momentum of saidflywheel means after the rotation of said shaft means is stopped; and f.linkage means for connecting said shaft means to the means for drivingthe counterweights so that when said shaft means is rotated in the firstdirection said linkage means causes the means for driving thecounterweights to drive the counterweights in the upper direction andwhen said shaft means is rotated in the second direction said linkagemeans causes the means for driving the counterweights to drive thecounterweights in the lower direction.
 6. The combination with a typicalcounterbalanced pump unit including in general a frame, a pump rodleading to a bottom hole pump, counterweights movably mounted on theframe for offsetting the weight of the pump rod, means for driving thecounterweights between upper and lower positions, and means for causingthe pump rod to move relative to the counterweights, of control meansfor controlling the means for driving the counterweights to allow thecounterweights to move between the upper and lower positions with equalor unequal speed in a smooth, even rate, said control means comprising:a. cammed means including shaft means rotatably mounted to the frame, afirst cylindrical cammed member fixedly mounted on a first end of saidshaft means, and a second cylindrical cammed member fixedly mounted on asecond end of said shaft means; b. cam follower means fixedly mounted onthe counterweights for coacting with said first cylindrical cammedmember when the counterweights are being driven to the upper position tocause rotation of said shaft means in a first direction and for coactingwith said second cylindrical cammed member when the counterweights arebeing driven to the lower position to cause rotation of said shaft meansin a second direction; c. linkage means connecting said shaft means tothe means for driving the counterweights so that when said shaft meansis rotated in the first direction said linkage means causes the meansfor driving the counterweights to drive the counterweighTs in the upperdirection and when said shaft means is rotated in the second directionsaid linkage means causes the means for driving the counterweights todrive the counterweights in the lower direction; d. flywheel meanscoactively mounted to said shaft means for temporarily storing themomentum of the rotation of said shaft means to cause rotation of saidshaft means to continue after the counterweights have reached the upperor lower position; e. stop means for stopping the rotation of said shaftmeans after a fixed amount of rotation; and f. clutch means fordissipating excessive momentum of said flywheel means after the rotationof said shaft means is stopped.